Gruithuisen's City in the Moon. 215 



which little explanation can be given, frequently come on with 

 the advancing lunar day ; and there is no antecedent improba- 

 bility in the idea that similar periodical alternations may be in 

 progress during the lunar night. Di.onysius has been selected 

 by Birt as a standard of magnitude among craters of a similar 

 character. — Ariadceus, and Ariadceus a, are a pair of craters at 

 the W. end of the great cleft which bears that name.* Sil- 

 berschlag, a crater 9f miles across, and of 8^° of brightness, 

 appears, with those already mentioned, in the diagram of this 

 rep-ion in our August number. There also we shall find 

 Agrippa (26), a fine ring, somewhat elliptical, 27 miles broad, 

 carrying a peak S., and interrupted by a little crater N. ; in 

 the steepest parts its interior slope amounts to 60° ; and it 

 ranges on the W. 6900 f., and 1000 f. more on the E., above 

 the interior. It a has several terraces, and a central hill. — 

 Godin (27) has a narrow but very steep ring of 8° light, equally 

 deep with Agrippa (Schr. makes it deeper), and of a somewhat 

 quadrilateral form : its breadth is 23 miles. It is connected 

 with Agrippa by ridges running in an oblique S.S.W. direction, 

 a peculiarity of which other instances might be given. Several 

 very defined craters lie in the neighbourhood. E. of Godin, we 

 find a small but very brilliant crater, Bhceticus b, which attains 

 9° of luminosity. Bhaiticus itself, which will be found in our 

 recent diagram, is an irregular ring, chiefly distinguished as 

 being bisected by the lunar equator, and as being one of the 

 few spots to which both Sun and Earth may be vertical ; all 

 these being, of course, comprised in an elliptical area, whose 

 centre is that of the Moon, and its boundary the extreme 

 amount of libration (which is greater in longitude than 

 latitude), as referred to the centre of the Earth (not to the 

 observer's position, in which it may be increased by parallax). 

 Yery strange, certainly, would be the aspect of the sky to any 

 one of ourselves, if we could conceive ourselves transported 

 there ; — the Sun describing a slow but cloudless course from 

 rising to setting, through the vertical region of the sky, and 

 often through the zenith itself; and the Earth oscillating 

 around that point for a short distance successively in every 

 direction — an enormous globe, waxing and waning with all the 

 features of the Moon, and turning every part in comparatively 

 rapid rotation to the eye of the spectator. The Bhceticus of 



* It should have been stated in our last number that the minute prolongation 

 of this cleft, noticed in p. 97 as having been discovered by Gruithuisen, has been 

 seen on several occasions by Messrs. Birt and Freeman. — I may be permitted also 

 to take this opportunity of rectifying two former mistakes, which have been 

 obligingly pointed out to me by Messrs. Knott and Proctor. The first occurs in 

 Int. Obs. vii. 134, where the E.A. of the Great Star of 1572 has been given at 

 4h. 19m. 57-7s., instead of 4>° 19' 577" (= Oh. 17m. 19-8s.) : the difference also 

 from Hind should have been, not 3m. 10s., but 3' 10". — The other is in Int. Obs. 

 x. 148, where, instead of density of the ring of Saturn, it should have been mass. 



